Method for the manufacture of double coated sheets with pressure-rupturable materials

ABSTRACT

TANDEM COATING OF PAPER WEB ON ONE SIDE FIRST WITH A COATING OF PRESSURE-RUPTURABLE ENCAPSULATED MATERIALS AND THEN WITH A COATING OF CLAY OVERLAYING THE COATING OF PRESSURE-RUPTURABLE MATERIALS, WHEREIN EACH COATING, WHILE WET WITH THE COATING COMPOSITION, IS DOCTORED TO METER THE COATING COMPOSITION AND TO UNIFORMLY DISTRIBUTE THE COATING COMPOSITION OVER THE SURFACE OF THE WEB.

1972 'r. w. BUSCH METHOD FOR THE-MANUFACTURE OF DOUBLE COATED SHEETSWITH PRESSURE-RUPTURABLE MATERIALS Filed Aug. 31, 1970 INVENTOB l V N'IO H g wm Rfig N3 mm w 23.3%

United States Batent 6 METHOD FOR THE MANUFACTURE OF DOUBLE COATEDSHEETS WITH PRESSURE-RUPTUR- ABLE MATERIALS Thomas W. Busch, Appleton,Wis., assignor to Appleton Papers, Inc., Appleton, Wis. Filed Aug. 31,1970, Ser. No. 68,417 The portion of the term of the patent subsequentto Oct. 20, 1987, has been disclaimed Int. Cl. B41m 5/16 US. Cl. 117-36.9 2 Claims ABSTRACT OF THE DISCLOSURE Tandem coating of paper web onone side first with a coating of pressure-rupturable encapsulatedmaterials and then with a coating of clay overlaying the coating ofpressure-rupturable materials, wherein each coating, while wet with thecoating composition, is doctored to meter the coating composition and touniformly distribute the coating composition over the surface of theweb.

This invention relates to the art of coated paper, and more particularlyto the method for the fabrication of a manifold sheet having twoseparate coatings on one side of the sheet in which one of the coatingsis formulated of a pressure sensitive material of the type described inthe patents hereinafter set forth.

In the United States Patents Nos. 2,299,693; 2,374,862; 2,548,366;2,712,507; 2,730,456; 2,730,457; 2,800,457; 2,929,736; 2,932,582;3,020,171; 3,104,980; 3,129,103; and 3,455,721, description is made of acopy process and materials for use in the practice of same in whichseparate coatings are provided on suitable carrier sheets in which oneof the coatings is formulated to contain a liquid reactant such as acolorless dye component dissolved in a liquid solvent and which isencapsulated in microscopic capsules uniformly distributed throughoutthe coating (hereinafter referred to as the emulsion coat), while theother coating is formulated of clay or other particulate substance whichis adapted to react with the liquid in response to release from thecapsules to form a colored image (hereinafter referred to as the mineralor clay coat). When the coating containing the encapsulated liquid ispositioned in surface contact with the clay coating, no color developsuntil pressure is applied by pen, pencil, stylus, typewriter key, dieimpression or the like, or by heat to rupture the capsules in the imagedareas whereby the liquid released from the ruptured capsule wets out theadjacent receptive material in the clay coating to develop the image.

In accordance with one form of paper of the type described, oftenreferred to in the art as carbonless copy paper, the paper is used in amanifold assembly in which the top sheet in the assembly is fabricatedwith only its underside coated with the emulsion coating, while thebottom sheet in the assembly is coated on its top side with only theclay coating. All of the sheets in between are coated on the undersidewith emulsion coating and on the top side with the clay or mineralcoating in two sidecoated sheets. Thus, an impression on the top sheetruptures the capsules contained on the underside of each of the sheetswhereby the encapsulated liquid thereby released wets out the adjacentclay coating to develop the image.

Because the micro-capsules are pressure sensitive and are capable ofbeing ruptured in response to pressure of the magnitude encountered inmechanical nips of a paper machine, it has been the practice to makeapplication of the microcapsular system as a separate operation applied3,705,049 Patented Dec. 5, 1972 ice onto the previously fabricated paperbase sheet. For this purpose, use has been made of a composition inwhich the micro-capsules are admixed with adhesive, lubricating pigmentsuch as talc, and cellulosic fibers which operate to protect thecapsules from premature rupture in the coating.

The described off-the-machine coating of the microcapsular system posesa number of requirements including (1) additional machinery for suchseparate off-the-machine coating; (2) additional floor space for suchseparate operations and equipment; (3) movement of paper from the papermaking machine to the described separate coating operation in whichpackaging, shipping and labor represent additional costs; (4) additionalwaste resulting from a two-stage process, and (5) procurement of paperas a separate commodity with its attendant costs, etc.

In my copending applications Ser. No. 795,663, filed on Jan. 31, 1969,now US. Patent No. 3,632,378, and Ser. No. 834,572, filed on Mar. 26,1969, now US. Patent No. 3,535,140, description is made of new andimproved methods and apparatus for preparing two-sided coated papersheets of the type described which represent significant improvementsover the prior art. In accordance with the methods described in thesecopending applications, use is made of tandem coatings in an off thepaper machine operation by which the emulsion coating and the claycoating are applied by separate stations in sequence on a single coatingmachine.

However, the methods as described in the aforementioned copendingapplications are adapted to form the mineral or clay coating and theemulsion on opposite sides of the paper web or sheet. Thus, they are notapplicable to a type of coated paper sheet which is known to the art asself-contained paper. The so-called selfcontained paper is a variationof carbonless copy paper of the type described above in which both theemulsion coating and the clay coating are formed on the same side of thepaper sheet with the emulsion coating being laid down prior to the claycoating. Thus, paper of this type can be used by placing it on theunderside of a sheet of untreated paper whereby an impression made onthe untreated paper causes rupture in the capsule coating of the treatedpaper whereby the fluid released thereby wets out the clay in thecoating overlaying the emulsion coating on the treated sheet to developthe image.

It is an object of the present invention to provide a new and improvedmethod for preparing self-contained paper of the type described in whichthe first coating is formed of a pressure sensitive material; in whichtwo separate coatings can be carried out in a single continuous multiplecoating process; and, in which the method can be carried out in a simpleand eflicient manner, with a minium amount of time, investment, labor,equipment and cost.

This and other objects and advantages of the invention will appearhereinafter, and, for purposes of illustration, but not of limitation,an embodiment of the invention is shown in the accompanying drawing inwhich:

FIG. 1 is a schematic elevational view of a coating method embodying theconcepts of the invention;

FIG. 2 is an enlarged view, partially in section, of a double coatedpaper sheet produced in accordance with the method illustrated in FIG.1.

Although the invention is addressed to the method and apparatus for thedual coating of paper base stock, the problem sought to be overcome bythis invention arises primarily by reason of the unique characteristicsof the compositions with which the base paper is coated.

Briefly described, the emulsion coating is formulated of an aqueouscomposition containing rupturable microscopic capsules of tanned gelatincontaining a liquid colorforming ingredient, such as a colorlessdyestuff dissolved in an organic solvent. There may be included withinthe emulsion coating composition, a substantial amount (up to 50% byweight of the capsules) of a coarse, solid particulate material, such askaolin clay and/or cellulose fibers suspended with the rupturablecapsules and in which a small of water-soluble binder may be dissolvedin the aqueous medium. For a more detailed description of the emulsioncoating, reference may be made to the examples in US. Patent No.2,711,375, and others of the patents heretofore set forth.

The clay coating comprises an aqueous system having an acid reactingmineral clay, such as attapulgite clay, or microfine solid particles ofan oil-soluble, acid-reactant organic polymer, in finely divided form,suspended therein, with or without other fillers such as calciumcarbonate, silica gel, satin white and the like, and a small amount ofnatural or resinous binder. For a more detailed description andformulation of the clay coating composition, reference may be made tothe examples in the aforementioned patents, particularly No. 3,455,721.

Referring now to the concepts of the invention in a method and apparatusfor the manufacture of self-contained sheets having dual coatings of thetype described on the same side of the paper base sheet, the paper rawstock, such as ll-pound manifolding bond, is supplied in the form ofrolls mounted for free rotational movement on a spindle 12 supported onthe unwind stand 14. The web 16 of raw stock paper is passed from theroll 10 over a series of idler rollers and guide rollers 18 to a firstcoating station 20.

The first coating station comprises an applicator roll 22 incommunication with a transfer roll 24 and a metering roll 26, the bottomportion of the transfer roll being immersed in a bath of the emulsioncoating composition in pan 28. The applicator roll 22 engages the bottomside of the paper web 16 as it passes between guide roll 30 and levelingroll 32 to apply an excess of the emulsion coating composition to thebottom side of the paper web. An amount of emulsion coating compositioncorresponding to a controlled excess above 4 /2 pounds per 3300 squarefeet is applied by the applicator and metering system at this firststation.

From the first coating station 20, the one side coated web is advanceddirectly to an air knife 34 which cooperates with the backing roll 36 tometer the coating to about 4 /2 pounds per 3300 square feet of the paperand to uniformly distribute the coating composition over the surfacethereof.

From the first coating station, the paper web, which has been turnedabout the roller 36, to position the coated side uppermost, is advancedthrough one section 42 of a drying oven maintained at a temperature ofabout 200 F. or higher while supported on an endless belt 44. The upperrun of the belt is supported on rollers 46 arranged in a substantiallyarcuate path through the dryer and, for this purpose, it is preferred tomake use of a foraminous belt or a belt formed of a vapor permeablematerial to enable the escape of water vapor therethrough when releasedfrom the coating. The endless belt 44 turns about rollers 48 and 50outside the dryer and the return run passes through the dryer section tomaintain temperature while being supported on a bottom run of rollers 52provided with a take-up roller 54 for maintaining the proper tension inthe supporting belt.

The paper base 16 with the dried emulsion coating 60 on the top sidethereof is passed from the drying oven 42 over a series of guide rollersand tcnsioning roller 62 and then over an assembly of turnover bars 61,63 and 65, which operate to turn over the continuous web whereby the topside containing the dried emulsion coating is on the underside of thesheet and ready for the second coating step. Any arrangement ofcommercially available turnover bars may be used in accordance with thepractice of the invention. As is known by those skilled in the art, suchturnover bars generally include an assembly of three rollers or bars,two of which are inclined with respect to horizontal and vertical axis.

From the turnover bars, the web having the treated emulsion coating onthe underside thereof is passed over a roller 67 to the second coatingstation, which is constructed similarly to the first coating station inthat it comprises an upper applicator roller 66 in accordance with theunderside of the web as the web passes between leveling roller 68 andguide roll 70. The applicator roller 66 is supported between a transferroller 72 and a metering roller 74 which takes up coating compositionfrom a bath in the coating pan 76 in which the bottom portion of thetransfer roller is immersed. The applicator roller is adjusted to applythe clay coating composition to the underside of the web overlaying thedried emulsion coating composition to a coating weight in a controlledexcess of about 4.5 pounds per 3300 square feet.

From the coating station 64, the coated web is advanced to a second airknife 78 and over the roller 80 which again operates in combination tometer to about 4.5 pounds per 3300 square feet the amount of coatingcomposition allowed to remain on the web and to distribute the claycoating overlaying the dried emulsion coating composition uniformlyacross the web.

From the air knife 78, the web which has been double coated first withthe emulsion coating and then with the clay coating overlaying the driedemulsion coating lowermost, is advanced over a suction apron 84 and thento an upper section 86 of the drying oven through which it is carried onthe surface of a supporting endless belt 88 in a relaxed state.

The upper run of the belt is supported on longitudinally spaced-apartcrosswise extending rollers 90 arranged in an arcuate path through thedryer. The belt continues to support the Web for a short distance beyondthe exit of the dryer. Thereafter, the belt turns downwardly and backabout rollers which lead through the dryer to a take up roller 92 whichis provided outside the dryer for adjusting the tension of the belt; aswith the belt 44, it is preferred to make use of a vapor permeable beltto enable the escape of vapors therethrough during passage through thedryer.

The web 16 containing the dried clay coating 94 overlaying the driedemulsion coating 60 is passed over a series of guide rollers and tensionrollers 96 to a wind up roller 98 mounted on a winder stand 100 andpowered to wind the coated web into the roller. Thus, the Web is drawnthrough the coating apparatus and dryer, and reel tension is developedin the wind up roller section.

It has been found that when use is made of premetering and air knives inthe processing of the applied coating composition, it becomes possibleto apply smooth coatings and dispense with the application and drying ofthe emulsion coating composition as a separate operation in advance ofthe application and drying of the clay coat. Under such circumstances,it becomes possible to apply the separate coating compositions insequence in a continuous operation on a continuously moving web therebyto obviate the necessity for making separate passes for each coatingoperation with a lapse of time between each coating application.Application of the clay coating composition in rapid sequenceimmediately following the application and drying of the emulsion coatingcomposition reduces the need for protective additives in the emulsioncomposition which have been necessary to protect the capsule coatedpaper during the handling of rolls which were required in a two-stageprocess on separate machines. Immediate application of the clay coatingcomposition over the freshly coated emulsion composition improves thebond between the two layers and thereby reduces the adhesive demand inthe clay coating composition. Both these effects thus improve theefficiency of capsule usage.

While the concepts of this invention find their best use in a continuousdouble coating operation in a single coating pass, it will be understoodthat many of the advantages and improvements of this invention will becapable of achievement by first coating the web with the emulsioncoating composition followed by drying in one pass and then coating theweb with the clay coating composition and drying in a subsequentseparate pass.

It will be further understood that numerous changes may be made in thedetails of formulation and operation, without departing from the spiritof the invention, especially as defined in the following claims.

I claim:

1. In the method of producing a double coated sheet having relativelyuniform smooth coatings on one side of the sheet in which the sheet isfirst coated with an aqueous emulsion-containing pressure-rupturablecapsule of a liquid color forming material and is then coated with anaqueous clay coating composition to form a clay coating overlaying theemulsion coating, the sequence of the steps of applying the emulsioncoating to one side of a moving paper web, doctoring the applied coatingwhile wet with an air knife to meter the coating and to uniformlydistribute the coating composition over the side of the web, drying theemulsion coating while the coated web is supported in a relaxed state ona continuous conveyor surface with the emulsion side uppermost, coatingthe same side of the coated web with a clay coating composition to forma clay coating overlaying the dried emulsion coating, doctoring the claycoating while wet with an air knife to meter the coating and touniformly distribute the clay coating composition over the Web and thendrying the clay coating.

2. The method as defined in claim 1 which includes the step of turningthe paper web over after drying the emulsion coating and beforeapplication of the clay coating composition whereby the clay coating isapplied to the same side of the paper web in one pass.

References Cited UNITED STATES PATENTS 3,535,140 10/1970 Busch 11736.22,730,457 1/1956 Green et a1. 117-36.8 3,573,085 3/1971 Hernstock11736.9

MURRAY KATZ, Primary Examiner US. Cl. X.R.

